The present invention relates to a process for providing molded plastic articles, in particular ophthalmic lenses, plastic articles and ophthalmic lenses themselves, and the use of metal organic compounds in such processes.
Recently, organic glass has begun to replace inorganic glass in optical elements, such as windows, prisms, cameras, television screens, telescopes, and ophthalmic lenses. The term ophthalmic lenses refers to corrective lenses as well as non-corrective lenses such as sunglasses. Organic glass possesses several favourable characteristics, including a lighter weight and better safety, e.g., better impact resistance, than inorganic glass.
Conventional materials used in organic glass include polystyrene resin, polymethyl methacrylate resin, and polycarbonate resin. However, these polymers have their respective disadvantages. For example, polymethyl methacrylate resin is liable to high moisture absorption, which changes its shape and refractive index. Also, polystyrene resin and polycarbonate resin have the disadvantage of giving rise to birefringence, light scattering, and loss of transparency with time. Furthermore, polymethyl methacrylate and polystyrene are neither scratch nor solvent resistant.
Organic glass made up of the products of the radical polymerization of poly(allyl carbonates) of polyhydroxy alcohols is also known, for example from European patent application 0 473 163. These polymers do not have the above-mentioned problems. However, when applying poly(allyl carbonates) of polyhydroxy alcohols in ophthalmic lenses increased mould damage occurs. Understood by mould damage is the damage incurred in a lens or in a mould on opening of the mould wherein the lens is formed.
Another known problem of such lenses is the occurrence of a surface defect of the casted organic glass that is known as xe2x80x9cfernsxe2x80x9d. The defects are called this way because they always appear in the shape of a fern leaf. The exact nature of these ferns and how they are being formed is unknown, but since the size of such ferns can vary from 0.5 to 30 cm2, they pose a real problem. It is possible to remove said ferns from the surface by polishing, however, such a process is undesired.
A further known problem is the uneven tinting of casted lenses with a colouring agent by means of a process of imbibing the lens, such processes being well-known in the art. The fact that the lens is coloured unevenly, may be associated with surface defects as well. A process wherein lenses are coloured more evenly is desired.
The Japanese patents JP 238151 and JP 09241336 teach the use of phosphorous compounds (phosphorous being a group 15 element according to the new IUPAC notation, with an electronegativity of about 2.1) as mould release agents. Common release agent present a number of problems when applied in the manufacturing of optical articles such as ophthalmic lenses. They regularly require high amounts to be effective and thereby negatively effect the mechanical and optical performance of the casted material. Furthermore they negatively affect the surface tension of the polymer, making the application of a coating (anti-scratch or other coating) and evenly tinting very difficult and its performance unreliable.
WO 96/24865 from the applicant teaches the use of diallyl phthalate type oligomers in curing compositions for ophthalmic lenses whereby mould damage in the production of said lenses is reduced.
Moulds used in today""s industry to prepare ophthalmic lenses from poly(allyl carbonate) of a polyhydroxy alcohol are only suited for compositions which result in ophthalmic lenses with identical refractive indices. A change in refractive index will result in a change in power of the lens when utilizing these moulds. Compositions resulting in higher refractive index lenses will require different moulds to obtain ophthalmic lenses with the same power. So, improvement of the properties of lenses by introducing certain oligomers and, optionally, comonomers cannot be achieved without limiting the refractive index of the resulting lens so that the moulds do not have to be changed.
An object of the present invention is to provide a process for providing moulded plastic articles whereby the mould damage, the occurring of ferns (ferning) and other tinting failures are being reduced.
The present invention relates to a process for providing a moulded plastic article comprising the step of polymerization casting of a curable composition comprising one or more polymerizable molecules or compounds which are preferably radically polymerizable and are preferably monomers, co-monomers and/or oligomers, for example poly(allyl carbonates) of polyhydroxy alcohols and methacrylic, acrylic, vinylic or allylic comonomers, in the presence of a mould release agent, which in turn comprises a metal organic compound, complexes and/or salts thereof, with the proviso that the metal of the metal organic compound is not Si or P. It is understood that the term metal as used here also includes transition elements. Furthermore it is noted that the term xe2x80x9cradical polymerizable monomersxe2x80x9d does not comprise conventional monomers that lead to urethane formation. Preferably, the invention relates to the process in which essentially all monomers are radically polymerizable. More preferably, the process involves the polymerization of a composition which consists essentially of radically polymerizable monomer(s), initiator(s), tinting agent(s), and the metal organic compound.
The mould damage, and ferns or other tinting failures in the production of the ophthalmic lens according to the present invention by using the claimed metal organic compounds is reduced without adversely affecting mechanical and/or optical properties of the optical articles, such as hardness and refractive index. Furthermore these metal organic release agents do not substantially negatively effect the surface tension of the polymer and monomer, and hence do not substantially negatively effect the adhesion of (anti-scratch) coatings onto the polymer surface. Preferred metal organic compounds are selected from organometallic compounds, complexes of metals, metal salts, and metal soaps. Most preferred are organometallic compounds wherein the metal is covalently bonded. The valency of the metal will typically vary from 1-6, a valency of 2-6 being preferred. Preferred metal organic compounds are of the formulae 1-111
wherein M is the metal as defined, X=O or S, and R1-R8 are independently selected from the group consisting of hydrogen, halogen, hydrocarbyl, halogen substituted hydrocarbyl, and 
wherein R9 is C2-C22 hydrocarbyl, preferably C4-12 hydrocarbyl, and X has the meaning as defined above,
whereby R1-R8 are optionally connected to form a ring structure.
Preferred compounds have a structure wherein R1-R8 are independently selected from essentially hydrogen, halogen, octoate, laurate, butyl, hexanoate, and decanoate. More preferred compounds are dibutyl metal dilaurates, dibutyl metal oxides, and metal 2-ethylhexanoates (octoates).
Without wishing to be bound to such theory, it appears that the electronegativity of the metal is an important factor for selecting metal organic compounds that are useful in the process according to the invention. Using the table of electronegativity of elements as calculated according to Allred and Rochow and as published in the textbook by Cotton and Wilkinson in Basic Inorganic Chemistry, ISBN# 0471-50532 3, Table 2-3, as a reference, the preferred metal of the metal organic compound has an electronegativy from 1.5 to 1.75. More preferred metals have an electronegativity, as calculated by Allred and Rochow""s method, of 1.6 to 1.73. Most preferred metals are Zn, Sn, and Co.
If used to produce ophthalmic lenses, the metal organic release agents must be completely soluble in the monomer to prevent the reduction of transmission of the lens.
The inventors have noted that the claimed metal organic compounds express release agent activity even at very low concentration, and are suitable as both internal, i.e. present in the polymerizable composition, release agents and external, i.e. applied directly to the mould, release agents. Preferably, the metal organic compounds are used as an internal release agent
If used as an external release agent, they may be applied to the mould prior to lens casting, for example, by any suitable methods such as spraying or dipping, either in the concentrated form, or as a solution in a solvent. Typically, if applied as a solution, the solvent is allowed to evaporate before the mould is actually used in the casting process.
If used as an internal release agent, the metal organic compounds can be introduced in the polymerizable composition in the pure form or as dissolution in a suitable medium. Such suitable medium is typically one monomer, or a mixture of monomers, to be used in the polymerizable composition. Although it is possible to combine the pure metal organic compound with other compounds (in the pure form) that are to be used in the composition, such as e.g. the initiator or the colouring agent, this is typically not desired since the metal organic compounds may have a destabilizing effect on such compounds, which may lead to hazardous situations. Preferably, the metal organic compounds are introduced into the polymerizable composition in the pure form or in the form of said dissolution in one or more monomers. For accurate dosing it is preferred to use a solution of the metal organic compound with a concentration of 0.001 to 50% w/w. More preferably 0,01 to 25% w/w, and even more preferably 0.05 to 20% w/w. Such solutions may supply all of the monomer to be polymerized, or, preferably, be combined with further monomer.
The metal organic compounds according to the invention are not meant to be used as radiation shielding compounds as described in, for instance, U.S. Pat. No. 5,856,415. Whereas radiation shielding compounds are typically used in an amount of greater than 15% by weight (% w/w) in order to be effective, the mould release agents are typically used in lower concentration. More preferably they are used in a concentration of less than 10% w/w, while most preferably they are used in an amount of less than 5% w/w. All based on the weight of the final lens.
Preferably, the metal organic compounds are used in such a quantity that the surface tension of the finished product is about equal to the surface tension of the mould that is used. More preferably, the surface tension of the mould is less than 37 mN/m to prevent the defects as described above from occurring. In case the casting composition is used in the casting of ophthalmic lenses using glass moulds, it is preferred to use the metal organic release agent in an amount such that the maximum required force to open the mould is 200N or less. More preferably, the required mould opening force is less than 90N, while a maximum force of 80N is most preferred. Another way to establish the desired amount of metal organic compounds in the ophthalmic lens casting process is by evaluation of the demoulding energy that is released upon opening of the mould. Preferably, the amount is chosen such that the demoulding energy is less than 0.15 Nm, more preferably less than 0.1 Nm. Typically the metal organic compound is used in a quantity from 0.0001 (1 ppm) to 5% w/w, more preferably 0.001 to 2% w/w, even more preferably 0.002 to 1% w/w, and most preferably 0.0025 to 1% w/w, based on the total weight of the casted composition.
The radical polymerizable molecules or compounds can be generally polymerized by either a method in which the polymerization is accomplished with heat or a method in which the polymerization is accomplished with light. As radical polymerizable monomers there can be used any widely known monomer having a radical polymerizing group without limitation.
Further radically polymerizable monomers may optionally be present in the curable composition up to 20% w/w. These comonomers may be methacrylic, acrylic, vinylic or allylic. Examples include methyl acrylate, methyl methacrylate, phenyl methacrylate, vinyl acetate, vinyl benzoate, diallyl isophthalate, diallyl terephthalate, diallyl adipate, and triallyl cyanurate.
The compositions of the present invention will typically contain a polymerization initiator in quantities ranging from 0.01 to 10 wt % as is known in the art. This initiator should be soluble in the other components present in the composition to be cured and capable of producing free radicals at a temperature which ranges from 30xc2x0 to approximately 100xc2x0 C. Examples of such initiators are organic peroxide and percarbonate initiators, especially diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, dibenzoyl peroxide, tert-butyl perbenzoate, benzoyl peroxide, lauryl peroxide, azobis(iso-butylonitrile) and azobis(2,4di-methylvaleronitrile). For the purpose of the present invention, it is preferable for the polymerization initiator to be present in the composition in quantities from about 1 to 8% w/w The initiators can be used either singly or in combination of two or more.
The curing of the polymerizable composition of the present invention can also be conducted by using a conventional photo polymerization initiator. As the photo polymerization initiator, any widely known compound can be used without limitation that is added for photopolymerizing the radical polymerizable monomers. Examples of the photopolymerization initiator that can be used in the present invention are Acetophenone initiators, such as 1-phenyl-2-hydroxy-2-methylpropane-1-one, hydroxycyclohexylphenyl ketone; Acylphosphine oxide initiators such as 2, 4, 6-trimethylbenzoyidiphenylphosphine oxide, 2,6-dichlorobenzoyidiphenyl-phospineoxide; Bisacylphosphine oxide initiators and dicarbonyl compounds.
The poly(allyl carbonates) of polyhydroxy alcohols may be used in the form of either monomers or oligomers and are of the conventional type. Monomers are usually obtained by using chloroformates. In this way, diethylene glycol diallyl carbonate can be obtained by reacting diethylene glycol bis(chloroformate) with allyl alcohol in the presence of an alkali, as described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., John Wiley and Sons, 1978, Vol. 2, p. 111. Monomers and oligomers of poly(allyl carbonates) of polyhydroxy alcohols can also be suitably obtained by means of transesterification reactions between diallyl carbonate and a polyhydroxy alcohol, as described in European patent application 0 035 304. In this way, monomers or mixtures of monomers and oligomers can be obtained, depending on the ratio of diallyl carbonate reagents to polyhydroxy alcohol. It is also possible to obtain mixed poly(allyl carbonates) of polyhydroxy alcohols by reacting a diallyl carbonate with a mixture of polyhydroxy alcohols in a transesterification reaction. These mixed poly(allyl carbonates) of polyhydroxy alcohols are also included in the present invention. Monomers of poly(allyl carbonates) of potyhydroxy alcohols are preferred for the ophthalmic lens of the present invention.
The polyhydroxy alcohols used in the preparation of poly(allyl carbonates) of polyhydroxy alcohols contain from 2 to 20 carbon atoms and from 2 to 6 hydroxy groups in the molecule. Examples of these alcohols are: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-dimethanol cyclohexane, 4,8-bis(hydroxyethyl) tricyclo(5,2,1 ,02,6)decane, xcex1,xcex1xe2x80x2-xylenediol, 1,4-bis(hydroxyethyl) toluene, 2,2-(bis(4-hydroxyethyl)phenyl) propane, pentaerythritol, trimethylol propane, dipentaerythritol, ditrimethylol propane, and tris(hydroxyethyl) isocyanurate. The following polyhydroxy alcohols are preferred: diethylene glycol, 1,4-dimethanol cyclohexane, pentaerythritol, and tris(hydroxyethyl) isocyanurate.
Examples of the diol include ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-dimethanol cyclohexane, 1,3-butanediol, neopentyl glycol, 1,3-cyclohexanediol, p-xylene glycol, and styrene glycol, and other aliphatic and aromatic diols. Branched diols are preferable to linear ones. Examples of such branched diols include 1,2-propylene glycol, 1,3-butanediol, neopentyl glycol, 2,3-butanediol, 1,4-pentanediol, 1,3-pentanediol, 1,2-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,5-hexanediol, 1,4-hexanediol, 1,3-hexanediol, 1,2-hexanediol, 2,3-hexanediol, 2,4-hexanediol, 2,5-hexanediol, and 3,4-hexanediol.
Examples of the polyols include aliphatic trihydric alcohols, such as glycerine and trimethylol propane, and aliphatic polyhydric alcohols, such as pentaerythritol and sorbitol.
Examples of polymerizable monomers that can favorably be used in the present invention include the following compounds of the conventional type.
That is, polyfunctional acrylate or methacrylate, such as diethylene glycol dimethacrylate, triethylene glycol dimethacrylate and 2,2-bis(4-methacryloyloxyethoxyphenyl)propane. Examples of other radical polymerizable monomers include unsaturated carboxylic acids such as (meth)acrylic acid, maleic anhydride, (meth)acrylic ester compounds such as methyl(meth)acrylate, benzyl(meth)acrylate, bisphenol-A di(meth)acrylate, urethane (meth)acrylate and epoxy(meth)acrylate; allyl compounds such as diallyl phthalate, diallyl terephthalate, diallyl carbonate and allyl diglycol carbonate; aromatic vinyl compounds such as styrene, xcex1-methylstyrene, vinyl naphthalene, and divinylbenzene; cyclohexyl diallyl ester oligomers, diallyl phthalate ester oligomers, and diallyl terephthalate ester oligomers. These monomers may be used in a single kind or being mixed together in two or more kinds.
For the production of ophthalmic lenses it is preferred to use a casting composition resulting in a lens with a refractive index of 1.45 to 1.55, more preferably 1.48-1.52, most preferably about 1.5.
The composition may also contain one or more conventional additives to act as ultraviolet light absorbers, dyes, pigments, and/or infrared light absorbers.